Container base



FIG. 1 is a bottom perspective view of a container base showing our new design;

FIG. 2 is a bottom plan view thereof; and,

FIG. 3 is a side elevation view thereof.

The broken lines showing of a bottle in FIGS. 1 and 3 are included for the purpose of illustrating environmental structure only and form no part of the claimed design. 

The ornamental design for a container base, as shown and described. 